Systemic Lupus Erythematosus (SLE) is an autoimmune disease, characterized by the production of unusual autoantibodies in the blood. These autoantibodies bind to their respective antigens, forming immune complexes which circulate and eventually deposit in tissues. This immune complex deposition causes chronic inflammation and tissue damage.
The precise reason for the abnormal autoimmunity that causes lupus is not known. Inherited genes, viruses, ultraviolet light, and drugs may all play some role. Genetic factors increase the tendency of developing autoimmune diseases, and autoimmune diseases such as lupus, rheumatoid arthritis, and immune thyroid disorders are more common among relatives of patients with lupus than the general population. Some scientists believe that the immune system in lupus is more easily stimulated by external factors like viruses or ultraviolet light. Sometimes, symptoms of lupus can be precipitated or aggravated by only a brief period of sun exposure.
Since patients with SLE can have a wide variety of symptoms and different combinations of organ involvement, no single test establishes the diagnosis of SLE. To help doctors improve the accuracy of diagnosis of SLE, eleven criteria were established by the American Rheumatism Association. These eleven criteria are closely related to the variety of symptoms observed in patients with SLE. When a person has four or more of these criteria, the diagnosis of SLE is strongly suggested. However, some patients suspected of having SLE may never develop enough criteria for a definite diagnosis. Other patients accumulate enough criteria only after months or years of observation. Nevertheless, the diagnosis of SLE may be made in some settings in patients with only a few of these classical criteria. Of these patients, a number may later develop other criteria, but many never do. The eleven criteria conventionally used for diagnosing SLE are:                1—malar over the cheeks of the face or “butterfly” rash        2—discoid skin rash: patchy redness that can cause scarring        3—photosensitivity: skin rash in reaction to sunlight exposure        4—mucus membrane ulcers: ulcers of the lining of the mouth, nose or throat        5—arthritis: two or more swollen, tender joints of the extremities        6—pleuritis/pericarditis: inflammation of the lining tissue around the heart or lungs, usually associated with chest pain with breathing        7—kidney abnormalities: abnormal amounts of urine protein or clumps of cellular elements called casts        8—brain irritation: manifested by seizures (convulsions) and/or psychosis        9—blood count abnormalities: low counts of white or red blood cells, or platelets        10—immunologic disorder: abnormal immune tests include anti-dsDNA or anti-Sm (Smith) antibodies, false positive blood tests for syphilis, anticardiolipin antibodies, lupus anticoagulant, or positive LE prep test, and        11—antinuclear antibody: positive ANA antibody testing        
Although the criteria serve as useful reminders of those features that distinguish lupus from other related autoimmune diseases, they are unavoidably fallible. Determining the presence or absence of the criteria often requires interpretation. If liberal standards are applied for determining the presence or absence of a sign or symptom, one could easily diagnose a patient as having lupus when in fact they do not. Similarly, the range of clinical manifestations in SLE is much greater than that described by the eleven criteria and each manifestation can vary in the level of activity and severity from one patient to another. To further complicate a difficult diagnosis, symptoms of SLE continually evolve over the course of the disease. New symptoms in previously unaffected organs can develop over time. Because conventionally there is no definitive test for lupus, it is often misdiagnosed.
Monitoring disease activity is also problematic in caring for patients with lupus. Lupus progresses in a series of flares, or periods of acute illness, followed by remissions. The symptoms of a flare, which vary considerably between patients and even within the same patient, include malaise, fever, symmetric joint pain, and photosensitivity (development of rashes after brief sun exposure). Other symptoms of lupus include hair loss, ulcers of mucous membranes and inflammation of the lining of the heart and lungs which leads to chest pain.
Red blood cells, platelets and white blood cells can be targeted in lupus, resulting in anemia and bleeding problems. More seriously, immune complex deposition and chronic inflammation in the blood vessels can lead to kidney involvement and occasionally failure requiring dialysis or kidney transplantation. Since the blood vessel is a major target of the autoimmune response in lupus, premature strokes and heart disease are not uncommon. Over time, however, these flares can lead to irreversible organ damage. In order to minimize such damage, earlier and more accurate detection of disease flares would not only expedite appropriate treatment, but would reduce the frequency of unnecessary interventions. From an investigative standpoint, the ability to uniformly describe the “extent of inflammation” or activity of disease in individual organ systems or as a general measure is an invaluable research tool. Furthermore, a measure of disease activity can be used as a response variable in a therapeutic trial.